Electroless plating of ruthenium and ruthenium-plated products

ABSTRACT

An electroless plating Ru bath for the deposition of Ru on the surface of a substrate comprises a Ru stock solution and hydrazine as a reducing reagent. Ru layers may be applied, for example, for use in membranes for the separation of hydrogen gas from mixtures of gases or to protect materials from corrosion. An example Ru stock solution comprises Ru chloride, hydrochloric acid, ammonia, nitrite salt, alkali hydroxide, and deionized water. The electroless plating bath may be applied to deposit ruthenium layers onto palladium layers to prepare Pd—Ru composite or alloy membranes or multilayer Pd—Ru composite or alloy membranes. Such membranes have example application to the separation of hydrogen from mixtures of gases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119 of U.S.Application No. 61/737664 filed 14 Dec. 2012 and entitled ELECTROLESSPLATING OF RUTHENIUM AND RUTHENIUM-PLATED PRODUCTS which is herebyincorporated herein by reference for all purposes.

FIELD OF THE INVENTION

This invention relates to electroless plating, in particular to platingbaths and associated methods for the electroless plating of rutheniumand to novel Ru-plated products including but not limited palladium-Rucomposite membranes useful for applications such as hydrogen separation.

BACKGROUND

Hydrogen may be used as an energy carrier. Hydrogen is also usedextensively to make products such as ammonia, methanol, gasoline,heating oil, and rocket fuel. There is a need for inexpensive andreliable ways to obtain pure hydrogen.

Currently, hydrogen is mainly produced via steam methane reforming,followed by conventional separation techniques, such as high and lowshift reactions followed by pressure swing adsorption. Membraneseparation using hydrogen-selective membranes is a cost-effective methodfor separating hydrogen from mixtures of gases at elevated temperatures.

Pd-based membranes prepared by electroless plating have been used forhydrogen separation. Such membranes can have high resistance to hydrogenembrittlement and oxidation, good thermal stability, favorable catalyticactivity for hydrogen dissociation and recombination, and appropriatehydrogen permeability. Because Pd is expensive and its hydrogenpermeability is generally inversely proportional to its thickness,Pd-based membranes are usually prepared in composite form comprisingthin Pd-based layers, to provide high hydrogen permselectivity.

The literature describes some Pd, Pd—Cu, and Pd—Ag membranes. Suchmembranes can be difficult to alloy into homogeneous layers due to thedifferent melting points of the metals which make them up. Suchmembranes also tend to be unstable at elevated temperatures. Inaddition, Pd and Pd—Ag composite membranes suffer severe hydrogenembrittlement problems at temperatures below 300° C. and 200° C.,respectively.

Pd—Ru alloy foils are more stable at both high and lower temperaturesthan other Pd-based membranes. However, Pd—Ru alloy is hard and istherefore difficult to form into foils. As a result, Pd—Ru alloy foilsare typically thick (>75 μm), limiting their application on alarge-scale due to the expense of Pd.

Electroless plating is an auto-catalytic process that uses a reducingagent to deposit a thin layer of material, such as copper, nickel,silver, gold, Pd, or Ru, on the surface of some solid substrate by meansof electrochemical reactions. Electroless deposition is typicallyperformed in an aqueous solution containing metal ions, a reducingagent, complexing and buffering agents, and stabilizers. Unlikeelectroplating methods, electroless plating does not require anexternally applied electric current to drive the deposition reactionElectrons derived from the heterogeneous oxidation of the reducing agentat a catalytically active region of the substrate surface reduce metalions to metal atoms, which deposit on the substrate surface. Under theright conditions, a continuous metal deposit can be obtained.

Electroless plating has several advantages over techniques, such asevaporation and sputtering. Compared to these other techniques,electroless plating uses materials and equipment that are relativelyinexpensive. Although electroless plating appears to be a simple andinexpensive technique, the chemical reactions occurring at the substratesurface can be complex. Conditions such as temperature, ionconcentration in the plating bath, and the duration of time thesubstrate is contacted with the plating bath can affect plating qualityand thickness. Electroless plating can be sensitive to contaminants.

Ru can be difficult to deposit by electroless plating because the Rucation typically exists in multiple oxidation states. This can result indisproportionation reactions that take place over desirableheterogeneous film growth on a substrate. Methods to deposit Ru byelectroless plating using various reducing reagents, such as sodiumhypophosphite and sodium borohydride, have been proposed in theliterature however, the layers of Ru deposited by such methods tend tobe of low quality (e.g. affected by severe hydrogen embrittlement and/orco-deposited impurities).

BRIEF DESCRIPTION OF THE DRAWINGS

An example embodiment illustrating an application of the invention isillustrated in the attached figure of the drawings. The figure disclosedherein is illustrative and non-limiting.

FIG. 1 is a schematic illustration showing a stainless steel tube ordisk with a porous ceramic base plated with a Pd—Ru composite membrane.

FIG. 2 is a sample image of a Pd—Ru composite membrane distributed on astainless steel disk.

FIG. 3 is a sample image of a Pd—Ru composite membrane distributed on astainless steel disk, as captured by a scanning electron microscope(SEM).

FIG. 4 is an example of the permeation flux and the selective permeationflux of hydrogen gas across a Pd—Ru composite membrane as a function oftime.

DETAILED DESCRIPTION

Throughout the following description specific details are set forth inorder to provide a more thorough understanding to persons skilled in theart. However, well known elements may not have been shown or describedin detail to avoid unnecessarily obscuring the disclosure. Accordingly,the description and drawings are to be regarded in an illustrative,rather than a restrictive sense.

One aspect of this invention relates to electroless plating of Ru. Thisaspect provides a bath for electroless plating of Ru comprising an Rustock solution and a hydrazine reducing agent. The bath has a pH of atleast 13. Such a bath may be applied, for example, to the production ofRu-based membranes useful for hydrogen separation or other purposes. TheRu-based membranes have many applications, including the separation ofhydrogen from mixtures of gases and the protection of surfaces used incorrosive environments from corrosion. Other aspects of this inventionprovide methods for depositing Ru onto the surface of a substrate byelectroless plating.

In an example embodiment, a Ru stock solution comprises a source of Ruions and a water soluble nitrite salt. In some embodiments the Ru stocksolution comprises a source of Ru ions, a water soluble nitrite salt,and any one or more of the following: hydrochloric acid, a complexingreagent, and an alkali hydroxide.

Ruthenium chloride is a preferred source of Ru ions, however, personsskilled in the art will recognize that other suitable sources of Ru ionssuch as, for example, ruthenium nitrate, K₂[Ru(NO)Cl₅], or[Ru(NO)(NH₃)₅]Cl₃ may be used in the alternative.

When mixed with Ru ions, the complexing reagent forms a Ru complex thatis stable but reducible under electroless plating bath conditions.NH₃H₂O is a preferred complexing reagent, however, persons skilled inthe art will recognize that other suitable complexing reagents that formstable but reducible complexes with Ru may be used in the alternative.

The alkali hydroxide comprises an alkali metal cation (e.g. Na⁺ or K⁺)and hydroxide anions (OH⁻). The alkali hydroxide is provided in anamount suitable to control pH. Sodium nitrite is the preferred watersoluble nitrite salt, however any suitable nitrite salt may be used.

An example Ru stock solution can be obtained by dispersing Ru chloridein deionized water and adding small amounts of HCl, ammonia, alkalihydroxide, and NaNO₂. In some cases, the molar ratio of ammonia/Ru is atleast 150, and in some cases is in excess of 200. The molar ratio of NO₂⁻/Ru may be at least 1, and in some cases is in excess of 5. In somecases, the molar ratio of NO₂ ⁻/Ru is in the range of 3 to 5.

For example, the Ru stock solution can comprise 1.0×10⁻³ M to 2.0×10⁻¹ MRuCl₃×H₂O (Ru mass, 38%), 4.0×10⁻² M to 5.0×10⁻¹ M HCl, 1.0 M to 21 MNH₃H₂O (28%), 1.0×10⁻¹ M to 1.0 M NaOH, and 4.0×10⁻²M to 4.5×10⁻¹ NaNO₂in deionized water. In some embodiments the concentration of Ru ions inthe stock solution is about 1.0×10³ M to about 2.0×10¹ M. In someembodiments, the Ru stock solution comprises 0.10% weight to 0.51%weight Ru, 0.15% weight to 1.46% weight HCl, 1.7% weight to 35.7% weightNH₃, 0.4% weight to 4% weight NaOH, and 0.28% weight to 3.11% weightNaNO₂ in deionized water. Further, in some embodiments, the Ru stocksolution comprises 1.8×10⁻² M RuCl₃×H₂O (Ru mass, 38%), 8.8×10⁻² M HCl,6.6 M NH₃H₂O (28%), 2.2×10⁻¹ M NaOH, and 5.7×10⁻² M NaNO₂ in deionizedwater.

The hydrazine reducing reagent is added to the Ru stock solution. Theresulting electroless plating Ru bath has a pH of at least 13. In somecases, the pH is in the range of 13 to 14. In some cases, the pH is atleast 13.3. In some cases the pH is not greater than 13.7. For example,the pH may be in the range of 13.3 to 13.7.

The molar ratio of hydrazine/Ru is at least 2 in some embodiments. Themolar ratio is typically kept below 30 and is typically in the range of5 to 20. However, this is not mandatory. In some cases the molar ratioof hydrazine/Ru is in excess of 30.

A stock solution as described above may be used to deposit a layer of Ruonto a substrate by electroless plating. Any of a wide variety ofmaterials may be used as a substrate. For example, the substrate maycomprise porous or nonporous stainless steel, porous ceramic, graphite,carbon, properly activated glass, Cr, Co, Au, Fe, Mo, Ni, Pd, Pt, Rh,Ru, Ag, Al, Sn, or W. In applications for which a Ru-containing layer isintended to be used for gas separation or similar applications thesubstrate may be gas-permeable (e.g. the substrate may be porous). Thesubstrate may have any suitable form. For some applications, substratesin the form of sheets, tubes or disks are convenient. To achieve uniformsurface coatings of Ru by electroless plating it is desirable that thesurface of the substrate be smooth.

Prior to using a bath to perform electroless plating of Ru the substratecan be activated with a catalyst, such as Pd nuclei, in order to shortenthe induction period at the beginning of Ru plating. For example,substrate activation may comprise one or more cycles of impregnation ofthe substrate in dilute Pd chloride solution and drying. This may befollowed by hydrogen reduction at approximately 450° C. for a suitabletime such as about 1 hour.

The electroless plating Ru bath may be used to deposit Ru onto asubstrate by heating the bath and immersing the substrate in the heatedbath. In some cases, the substrate is added to the Ru stock solution,heated, and the hydrazine reducing reagent is then added to the heatedbath. The temperature of the electroless plating Ru bath may, forexample be 40° C. or higher. In some cases the bath has a temperature of70°C. or more. The temperature is typically kept below 70°C. In somecases, the temperature is in the range of 50°C. to 60° C.

When the desired amount of Ru plating is achieved, the substrate can beremoved from the bath.

Example applications of the electroless plating Ru bath and the methodfor depositing Ru on a substrate surfacing using electroless platinginclude plating substrates to be used in hydrogen gas separation andplating substrates used in corrosive environments. Due to the thermalstability of Ru, stainless steel, and ceramic, these materials areideally suited for use in high temperature hydrogen gas separation. Forexample, a hydrogen separation membrane may comprise a porous substrate(of e.g. stainless steel and/or ceramic) supporting a thin layercomprising Ru and Pd. The Ru may be deposited by electroless plating asdescribed above. The Pd in the membrane may also be deposited byelectroless plating, for example, Pd may be deposited using any knownelectroless plating technique for Pd, such as that described by Anwu Li,et al. in Preparation of thin Pd-based composite membrane on planarmetallic substrate: Part II: Preparation of membranes by electrolessplating and characterization, Journal of Membrane Science 306 (2007)159-165. Pd may be deposited in other ways in the alternative.

Another application uses the novel electroless plating Ru bath disclosedherein to prepare Pd—Ru composite and alloy membranes used for theseparation of hydrogen from gaseous mixtures.

FIG. 1 shows a substrate 11 comprising a porous base 12 coated with athin layer of Pd and Ru 13. Layer 13 may comprise one or more layers ofPd deposited on the porous base 12 using any suitable technique forelectroless plating of Pd and one or more layers of Ru using anelectroless plating bath as disclosed herein.

After deposition the one or more Pd layers and the one or more Ru layersmay be treated, for example by a heat treatment to yield layer 13. Forexample, a Pd—Ru composite membrane or multilayer Pd—Ru compositemembrane may be annealed in situ during hydrogen permeation at atemperature of approximately 600° C. to yield a Pd—Ru alloy membrane.

Pd—Ru composite and alloy membranes maybe prepared by plating asubstrate with thin layers of Pd and Ru in alternation. In some cases,the substrate is first plated with Pd using any known electrolessplating method, such as that described by Li, et al. cited above. Thesubstrate is then plated with Ru using the electroless plating Ru bathand method disclosed herein. Ru is a more robust metal and is morechemically inert than Pd making it ideally suited to be plated such thatthe exposed layer is the Ru layer. However, in the alternative, thePd—Ru composite membrane can be prepared by first plating the substratewith Ru and subsequently plating the substrate with Pd.

In some embodiments, the overall Ru composition of the Pd—Ru compositeand alloy membrane is in the range of about 1% weight to about 12%weight. In some cases, the overall Ru composition is in the range ofabout 3% weight to about 8% weight In some embodiments, the overall Pdcomposition of the Pd—Ru composite and alloy membrane is in the range ofabout 88% weight to about 99% weight. In some cases, the overall Pdcomposition is in the range of about 92% weight to about 97% weight.

In some embodiments, the thickness of the Ru layers of the Pd—Rucomposite and alloy membrane is in the range of about 0.1 μm to about2.5 μm. In some embodiments, the thickness of the Pd layers of the Pd—Rucomposite and alloy membrane is in the range of about 1 μm to about 3μm. In some embodiments, there are one or more layers of each of Pd andRu.

In some embodiments, a membrane layer of one or more metals other thanPd and Ru may be prepared. Such additional deposited metals may alterthe composition of the membrane layer resulting after heat treatment ofthe deposited metals. For example, a Pd—Ag—Ru composite membrane or aPd—Ag—Ru alloy membrane may be prepared by electroless deposition of oneor more layers of each of Pd, Ru and Ag. The electroless plating bathdescribed herein may be applied for deposition of the Ru layers. Forexample, a Pd—Ag—Ru membrane may be prepared by sequentially, and in anyorder, plating a substrate with layers of Pd, Ag, and Ru. The substratemay be plated with Pd and Ag using known electroless plating methods,such as that described by Li, et al. cited above and by RajkumarBhandark, et al. in Pd—Ag membrane synthesis: The electroless andelectro-plating conditions and their effect on the deposits morphology,Journal of Membrane Science 334 (2009) 50-63. In some cases, thePd—Ag—Ru composite membrane is then annealed in situ during hydrogenpermeation to yield a Pd—Ag—Ru alloy membrane.

EXAMPLE 1 Ru Stock Solution Preparation

0.65 g of RuCl₃×H₂O (Ru mass, 38%) was dispersed in deionized water and1.0 mL of HCl (36%) was then added to form a suspension solution. Whenthe suspension solution became clear, 60 mL NH₃H₂O (28%), 1.2 g NaOH,and 0.53 g NaNO₂ were added. The final volume of the Ru stock solutionwas brought to 135 mL by adding deionized water.

EXAMPLE 2 Ru Electroless Plating at 60° C.

A solid stainless steel sheet with an area of approximately 2.0 cm² anda thickness of 0.4 mm was ultrasonically cleaned with acetone and waterto remove any organic contaminants. The sheet was then activated byimpregnating it with a solution of PdCl₂ followed by a reduction inhydrogen at 400° C. to 450° C. The sheet was then placed in a glass vialwith the activated surface facing upwards. 4.0 mL Ru stock solutionprepared as in Example 1 was then added to the vial. The vial was heatedin a 60° C. water bath. When the solution in the vial reached 60° C.,1.0 mL of 0.5 M hydrazine solution was added to the vial and thesolution was stirred. Gas bubbles quickly formed in the solution,indicating that Ru plating was occurring. After 30 minutes of plating,the sheet was removed from the vial, rinsed with deionized water, anddried in an oven at 120° C. for 2 hours. The thickness of the Ru filmformed on the sheet was approximately 1.9 μm (estimated by comparing theweight of the sheet before and after plating). The sheet was observedunder a SEM and the Ru film appeared to be continuously and uniformlydistributed on the sheet.

EXAMPLE 3 Ru Electroless Plating at 50° C.

A solid stainless steel sheet, cleaned and activated in the same batchas the sheet in Example 2, was placed in a glass vial, in 4.0 mL of theRu stock solution prepared in Example 1. The vial was heated in a 50° C.water bath. When the solution in the vial reached 50° C., 1.0 mL of 0.5M hydrazine solution was added to the vial and the solution was stirred.After 30 minutes of plating, the sheet was removed from the vial, rinsedwith deionized water, and dried in an oven at 120° C. for 2 hours. Thethickness of the Ru film formed on the sheet was approximately 1.1 μm(estimated by comparing the weight of the sheet before and afterplating). The sheet was observed under SEM and the morphology,microstructure, and quality of the Ru layer appeared to be similar tothe sample prepared in Example 1.

EXAMPLE 4

Ru Electroless Plating at 85° C.

A solid stainless steel sheet, cleaned and activated in the same batchas the sheet in Example 2, was placed in a glass vial, in 4.0 mL of theRu stock solution prepared in Example 1. The vial was heated in a 85° C.water bath. When the solution in the vial reached 85° C., 1.0 mL of 0.5M hydrazine solution was added to the vial and the solution was stirred.After 300 minutes, the sheet was removed from the vial, rinsed withdeionized water, and dried in an oven at 120° C. for 2 hours. No Rudeposition was observed.

EXAMPLE 5 Pd—Ru Alloy Membrane Preparation

A porous stainless steel disk was polished, etched, coated, andactivated as described in Example 2. The disk was first plated with Pdusing the known electroless plating Pd bath described in Li, et al. Thethickness of the Pd plating was approximately 6.5 μm. Ru wassubsequently plated on top of the Pd as described in Example 1. After 30minutes of plating, the thickness of the Ru layer was approximately 0.4μm. The Pd—Ru composite membrane was then annealed in situ duringhydrogen permeation at 600° C. Hydrogen permeance increased with timeand became steady after 24 hours, suggesting that a Pd—Ru alloy wasachieved. The overall thickness of the resulting Pd—Ru alloy membranewas 6.9 μm. The Pd—Ru alloy membrane was approximately 5% weight Ru and95% weight Pd. The hydrogen permeability of the Pd—Ru alloy membrane wasapproximately 20% higher than that of a Pd membrane annealed in situduring hydrogen permeation at a temperature of 550° C.

EXAMPLE 6 Ru-Plated Product

The Ru-plated stainless steel sheet prepared in Example 1 and anon-plated stainless steel sheet with the same area and thickness as thesample used in Example 1 were both placed into a 1000 mL solution of 70%weight H₂SO₄ maintained at 100° C. After one week, the non-platedstainless steel sheet had completely disappeared due to acid corrosion.After one month, no evident corrosion of the Ru-plated stainless steelsheet was observed.

EXAMPLE 7 Pd—Ru Composite Membrane Hydrogen Gas Permeability andSelectivity

A porous stainless steel disk with a diameter of approximately 5.0 cmand a thickness of 1.37 mm was cleaned and activated as described inExample 2. The disk was first plated with Pd using the known electrolessplating Pd bath described in Li, et al. The disk was then cleaned withdeionized water, dried in an oven at 50° C., and placed in a glass vial.4.5 mL of a Ru stock solution comprising 1.8×10⁻² M RuCl₃×H₂O (Ru mass,38%), 8.8×10⁻² M HCl, 6.6 M NH₃H₂O (28%), 2.2×10⁻¹ M NaOH, and 5.7×10⁻²MNaNO₂ was added to the vial containing the Pd—plated disk. 9.0 mL ofdeionized water and 1.0 mL of 2.0 M aNaOH solution were added to thevial. The vial was heated in a 55° C. water bath. When the solution inthe vial reached 55° C., 0.5 mL of 1.0 M hydrazine solution was added tothe vial and the solution was stirred. After 30 minutes of plating, thedisk was removed from the vial, rinsed with deionized water, and driedin an oven at 120° C. for 2 hours. The thickness of the Pd—Ru filmformed on the disk was approximately 6.4 μm (estimated by comparing theweight of the sheet before and after plating). FIG. 2 shows the Pd—Rucomposite membrane after preparation. The disk was observed under a SEMand the Pd—Ru composite film appeared to be continuously and uniformlydistributed on the disk, as shown in FIG. 3.

FIG. 4 shows the permeation flux of hydrogen gas across the Pd—Rucomposite membrane at a temperature between 350° C. to 400° C. for over1000 hours. The difference in pressure across the membrane was 1 bar.After approximately 50 hours, the permeation flux of hydrogen gas acrossthe membrane was approximately 13 m³/(m²h). The membrane was stable over1000 hours.

Also shown in FIG. 4 is the selective permeation flux of hydrogen gasacross the Pd—Ru composite membrane. A mixture of 75% hydrogen gas and25% nitrogen gas was applied across the membrane at temperatures between350° C. to 400° C. for over 1000 hours. The difference in pressureacross the membrane was 1 bar. After approximately 50 hours, thepermeation of hydrogen gas was a factor of approximately 15,000 greaterthan the permeation of nitrogen gas across the membrane. The membranewas stable over 1000 hours.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout thedescription and the claims:

-   -   “comprise”, “comprising”, and the like are to be construed in an        inclusive sense, as opposed to an exclusive or exhaustive sense;        that is to say, in the sense of “including, but not limited to”.    -   “connected”, “coupled”, or any variant thereof, means any        connection or coupling, either direct or indirect, between two        or more elements; the coupling or connection between the        elements can be physical, logical, or a combination thereof.    -   “herein”, “above”, “below”, and words of similar import, when        used to describe this specification shall refer to this        specification as a whole and not to any particular portions of        this specification.    -   “or”, in reference to a list of two or more items, covers all of        the following interpretations of the word: any of the items in        the list, all of the items in the list, and any combination of        the items in the list.    -   the singular forms “a”, “an”, and “the” also include the meaning        of any appropriate plural forms.

Words that indicate directions such as “vertical”, “transverse”,“horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”,“outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”,“top”, “bottom”, “below”, “above”, “under”, and the like, used in thisdescription and any accompanying claims (where present) depend on thespecific orientation of the apparatus described and illustrated. Thesubject matter described herein may assume various alternativeorientations. Accordingly, these directional terms are not strictlydefined and should not be interpreted narrowly.

While processes or blocks are presented in a given order, alternativeexamples may have steps or blocks presented in a different order.Processes or blocks may be deleted, moved, added, subdivided, combined,and/or modified to provide alternative embodiments (includingsubcombinations of described methods). Each of these processes or blocksmay be implemented in a variety of different ways. Also, while processesor blocks are at times shown as being performed in series, suchprocesses or blocks may instead be performed in parallel, or may beperformed at different times where this is technically practical.

Where an element or component (e.g. a solvent, solute, assembly, device,substrate, catalyst, activator, etc.) is referred to above, unlessotherwise indicated, reference to that component (including a referenceto a “means”) should be interpreted as including as equivalents of thatcomponent any component which performs the function of the describedcomponent (i.e., that is functionally equivalent), including componentswhich are not structurally equivalent to the disclosed structure whichperforms the function in the illustrated exemplary embodiments of theinvention.

Specific examples of systems, methods and apparatus have been describedherein for purposes of illustration. These are only examples. Thetechnology provided herein can be applied to systems other than theexample systems described above. Many alterations, modifications,additions, omissions and permutations are possible within the practiceof this invention. This invention includes variations on describedembodiments that would be apparent to the skilled addressee, includingvariations obtained by: replacing features, elements and/or acts withequivalent features, elements and/or acts; mixing and matching offeatures, elements and/or acts from different embodiments; combiningfeatures, elements and/or acts from embodiments as described herein withfeatures, elements and/or acts of other technology; and/or omittingcombining features, elements and/or acts from described embodiments.

It is therefore intended that the following appended aspects and claimshereafter introduced are interpreted to include all such modifications,permutations, additions, omissions and sub-combinations as mayreasonably be inferred. The scope of the claims should not be limited bythe preferred embodiments set forth in the examples, but should be giventhe broadest interpretation consistent with the description as a whole.

What is claimed is:
 1. A method for depositing Ru onto a surface of asubstrate, the method comprising: preparing an electroless plating bathhaving a pH of at least 13 comprising: a Ru stock solution; and ahydrazine reducing reagent; and contacting the substrate with theelectroless plating bath.
 2. A method according to claim 1, wherein theRu stock solution comprises: a source of Ru ions; and a water solublenitrite salt.
 3. A method according to claim 2, wherein the electrolessplating bath further comprises one or more of: hydrochloric acid; acomplexing reagent; and an alkali hydroxide.
 4. A method according toclaim 3, wherein the source of Ru ions comprises a chloride or nitrateof Ru.
 5. A method according to claim 3, wherein the complexing reagentcomprises ammonia.
 6. A method according to claim 5, wherein the molarratio of ammonia/Ru is at least
 150. 7. A method according to claim 6,wherein the molar ratio of ammonia/Ru is at least
 200. 8. A methodaccording to claim 7, wherein the alkali hydroxide comprises sodiumhydroxide or potassium hydroxide.
 9. A method according to claim 2,wherein the water soluble nitrite salt comprises sodium nitrite orpotassium nitrite.
 10. A method according to claim 2, wherein the molarratio of nitrite/Ru is at least
 1. 11. A method according to claim 2,wherein the molar ratio of nitrite/Ru is in the range of 3 to
 5. 12. Amethod according to claim 1, wherein the molar ratio of hydrazine/Ru isat least
 2. 13. A method according to claim 12, wherein the molar ratioof hydrazine/Ru is in the range of 5 to
 20. 14. A method according toclaim 1, wherein the pH of the electroless plating of the bath is in therange of 13 to
 14. 15. A method according to claim 14, wherein the pH isin the range of 13.3 to 13.7.
 16. A method according to claim 1,comprising maintaining a temperature of the electroless plating bath ata temperature of at least 50° C.
 17. A method according to claim 16,comprising maintaining a temperature of the electroless plating bath ata temperature of at least 60° C.
 18. A method according to claim 1,wherein the Ru stock solution comprises an aqueous solution of: 1.0×10⁻³M to 2.0×10⁻¹ M RuCl₃.×H₂O (Ru mass, 38%); 4.0×10⁻² M to 4.0×10⁻¹ M HCl;1.0 M to 21 M NH₃.H₂O (28%); 1.0×10⁻¹ M to 1.0 M NaOH; and 4.0×10⁻² M to4.5×10⁻¹ M NaNO₂.
 19. A method according to claim 1, wherein the Rustock solution comprises an aqueous solution of: 0.10% weight to 0.51%weight Ru; 0.15% weight to 1.46% weight HCl; 1.7% weight to 35.7% weightNH₃; 0.4% weight to 4% weight NaOH; 0.28% weight to 3.11% weight NaNO₂.20. A method according to claim 19, wherein the substrate comprisesstainless steel.
 21. A method according to claim 19, wherein thesubstrate comprises a ceramic.
 22. A method according to claim 21,wherein the substrate is porous.
 23. A method according to claim 19,comprising activating the substrate with a metal catalyst beforecontacting the substrate with the electroless plating bath.
 24. A methodaccording to claim 23, wherein the metal catalyst comprises Pd.
 25. Amethod according to claim 1 applied for preparing a Pd—Ru compositemembrane, the method comprising: prior to contacting the substrate withthe electroless plating bath, plating a surface of a substrate with Pdusing electroless plating; wherein the electroless plating bath has a pHof at least
 13. 26. A method according to claim 25, wherein theelectroless plating bath comprises: a source of Ru ions; and a watersoluble nitrite salt.
 27. A method according to claim 26, wherein theelectroless plating bath comprises: hydrochloric acid; a complexingreagent; and an alkali hydroxide.